[HermanLee]

I've been trying my AF540 wirelessly with my K20D
and I just noticed something weird.
How come the Shake Reduction automatically OFF right after I press FN , Down button, and then Wireless Flash?
I've tried several wireless flash mode and all show that the Shake Reduction is turned OFF.

Is this normal?
If yes, why does Pentax has to turn it off? Any explanation?

Thanks,

[flyer]

It is normal. As to the "why", who knows...

[creampuff]

The duration of the flash exposure will freeze motion so there is no advantage to have Shake Reduction.

[kenyee]

The duration of the flash exposure will freeze motion so there is no advantage to have Shake Reduction.

Yep, that's what I believe the thought process was. They probably used the extra CPU cycles to do the commander mode pulses.
A flash's "pulse" will freeze motion, so if you're using a flash, the pulse (roughly 1/1000 to 1/5000 to 1/25000 depending on power level) will freeze any motion. Try taking a picture of a rotating ceiling fan or fan with a flash and your camera set to 1/30sec...

[pentaxmz]

The duration of the flash exposure will freeze motion so there is no advantage to have Shake Reduction.

Exactly.

The average or typical 'speed' of a xenon flash tube is around 1/15000 second (some flash as high as [but not limited to] 1/25000 second). That is plenty of 'speed' to freeze nearly anything. Try this: Turn off your lights and take a flash photo of a fan; you can freeze motion the blades, even at the fan's highest speed! There are lot's of fun things to do with a flash.

Besides SR being useless in flash mode, I'm not sure 'why' the engineers decided to turn it off automatically..... perhaps to save on wear/tear, or save battery life? It is also possible that SR would introduce ghosting, especially if the Pentax flash has a lag time glow. So allowing SR to stay on in flash mode would be bad.

Only someone from Pentax can answer this question.

[Zebooka]

The duration of the flash exposure will freeze motion so there is no advantage to have Shake Reduction.

Yes and no.

If I want to a photo with 1"-1/30 sec (slow sync), then it will be quite useful.

[HermanLee]

The duration of the flash exposure will freeze motion so there is no advantage to have Shake Reduction.

This makes sense.
Thanks guys. Now I have to practice more.

[Jewelltrail]

HermanLee: NO Shake Reduction w/ Wireless Flash?
I've been trying my AF540 wirelessly with my K20D
and I just noticed something weird.
How come the Shake Reduction automatically OFF right after I press FN , Down button, and then Wireless Flash?
I've tried several wireless flash mode and all show that the Shake Reduction is turned OFF.

Is this normal?
If yes, why does Pentax has to turn it off? Any explanation?

Thanks,

Pentax uses similar reasoning with their remote feature, which is accessed with the function button, then the up arrow. Once you enable the remote, you forfeit the use of SR--the thinking clearly being the camera must be on a tri-pod, hence no utility for the SR.

[simico]

Yes and no.

If I want to a photo with 1"-1/30 sec (slow sync), then it will be quite useful.

SR is not deactivated for slow sync flash shots.

From the Pentax K-m FAQ:
Q: Will the Shake Reduction (SR) function work with slow synchronization of the flash?
A: Yes, it will function.

[soccerjoe5]

While flash may freeze the subject, the ambient/environment may be out of your control. I'd love to use SR in low shutter speeds for my outdoor environmental portraits. As the sun goes down, my shutter speeds drop. The subject is well exposed and frozen but my background won't always be as sharp because of the slow shutter speed (and it won't be affected by my lights).